Two-toed sloths' 'lazy' sex life revealed

two-toed Hoffmann's sloth A third of male Hoffman's two-toed sloths successfully sired offspring with more than one female

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The hidden sexual habits of Hoffmann's two-toed sloths have been revealed by scientists.

Mating activity of the "lazy" mammals was analysed in Costa Rica to assess the effect of a sedentary lifestyle.

Ecologists discovered a mating system where male sloths did not monopolise females but did show signs of defending some territory.

The study could help scientists understand how to protect other species threatened with habitat fragmentation.

The findings were published in the journal Animal Behaviour.

"It's not a total free for all," said one of the team, Dr Zach Peery.

Although sloth physiology and anatomy is well understood, the behaviour of sloth species is not, said Dr Jonathan Pauli, who co-authored the University of Wisconsin study with Dr Zach Peery.

When sloths ruled the earth

two-toed Hoffmann's sloth

Relatives of this two-toed Hoffmann's sloth once lived on the ground, rivalling the mammoths for size and had fearsome 50cm claws. From fossils, experts have learned more about the distant but formidable members of the sloth family.

"One of the real highlights...for a cryptic mammal like this is the ability for us... to almost get a census of these populations," he said.

The research was part of an ongoing monitoring programme in which males and females across the study site were located, tagged and genetically tested.

95 adult two-toed sloths, 32 subadults and 30 juveniles were captured and monitored for the study.

By testing for paternity and mapping the distribution of related individuals, the ecologists were able to piece together the population's mating behaviour.

The male home ranges contained an average of three females and the females usually appeared within the home range of more than one male.

The results showed that 36% of adult males sired offspring with at least two females, demonstrating that sloths are not monogamous.

"Because they're highly sedentary we thought that the males most probably wouldn't be able to vigorously defend a harem of multiple females," said Dr Zach Peery.

But the ecologists found evidence that the males monopolise space in certain core territorial areas, suggesting that their mating system is a complicated combination of polygyny, whereby one male monopolises many females, and promiscuity.

Two-toed Hoffmann's sloth The sloth study could help save other species that are facing the threat of habitat destruction

"They're not necessarily just puppy dogs, they will battle and we do find males with considerable facial scars so although there is overlap and although it's a somewhat more flexible mating system... there is structure to it," said Dr Peery.

There are a number of benefits to promiscuous mating systems for mammals, particularly from a female point of view, he said.

These range from the female not putting all of her "eggs in one basket with one male" to the reduced risk of infanticide.

"We are suggesting that the sedentary nature of sloths could be an additional reason," Dr Peery told BBC Nature.

The study site mirrors a type of habitat that is increasingly prevalent in central America, with a mixture of shade-grown cacao plantation, pasture, and fruit monoculture, which may prove an important combination for conservationists to understand in the future.

"There have been a number of different studies both in tropical forests in Asia and central America that have shown that biodiversity tends to be higher...in shade-grown agricultural systems," said Dr Peery.

The project is now turning its attention to the three-toed sloth which is found in the same area.

"If you can believe it, the three-toed sloth is even more sedentary and docile than the two-toed sloth," Dr Pauli told the BBC.

The "lazy" disposition of sloths makes them comparatively straightforward to study and they may hold the key to understanding how to protect other species that are threatened with habitat loss.

"Their dispersal across fragmented habitats is much lower so presumably they'll be a nice bellwether for other species," he said.

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